- Category: HIV/AIDS Epidemiology & Mortality
- Published on Wednesday, 15 February 2017 00:00
- Written by Gus Cairns
HIV incidence has started to tumble in the Rakai cohort, one of the best-studied groups of people in Africa, according to a report at the Conference on Retroviruses and Opportunistic Infections this week in Seattle. The annual HIV infection rate has fallen 40% in the last 4 years, researchers said. A combination of factors -- including wider availability of antiretroviral therapy, increased male circumcision, and later age of sexual debut in young people -- all appear to be contributing to this decline.
Presenter Mary Grabowski from Johns Hopkins confirmed that this is the first time a population-level decline in HIV incidence in the Rakai cohort has been observed.
The Rakai Community Cohort Study, in a corner of southern Uganda, is probably the longest-studied group of people living with, and at risk for, HIV in a low-income setting. This study, which dates from 1994-1995 and was built upon an even older one dating from 1989, enrolls every consenting adult aged 15-49 living in a 50-village territory. It regularly "tops itself up" with new members, keeping a level of about 12,000 participants. Rakai has hosted many pioneering HIV studies, ranging from the first study to show conclusively that HIV treatment reduced infectiousness, to one of the 3 landmark randomized studies of medical male circumcision for HIV prevention.
Rakai was chosen as a site because it was the area first and hardest hit by HIV in Uganda. In 1989 it had an HIV prevalence of over 20%, only surpassed since then by the later hyper-epidemic in southern Africa in the late 1990s.
HIV prevalence fell to 13% by the mid-1990s and has stayed pretty steady at that level ever since. At the time, the fall in prevalence was ascribed to the success of behavior change programs, but it was probably more due to deaths among the first wave of people infected during the peak of HIV incidence in the mid-1980s.
Incidence -- the rate of new infections among a population -- is a better guide to whether HIV epidemics are truly growing or shrinking, though true incidence is quite difficult to establish, as it is affected by testing rates. However, in situations with an established HIV epidemic and high rates of testing, as in Rakai, new diagnoses are a reasonable surrogate for incidence. And in the last 4 years there is no doubt that it has decreased.
The Present Study
Data were collected between 1999 and 2016 in 12 surveys from 30 communities in the Rakai Community Cohort. Incidence was compared at 7 particular time-points between 2004 and 2016, and compared with incidence prior to 2004.
Over this period 33,937 people took part; including 17,870 initially HIV-negative people and 16,067 living with HIV. Of the HIV-negative people, 931 (5.2%) tested HIV-positive during 94,427 person-years of follow-up, for an annual incidence of just under 1%.
Antiretroviral therapy (ART) started to become available in Rakai by 2004, and by 2016, 69% of people with HIV in the cohort were taking ART. This has led to an increase in the proportion of HIV-positive people in the community who are virally suppressed. This proportion -- including the undiagnosed and those not on ART -- rose from 42% in 2009 to 75% by 2016, and thus achieved the UNAIDS 90-90-90 target.
At the same time, the rollout program of medical male circumcision meant that the proportion of men who were circumcised rose from 15% in 1999 to 59% in 2016.
A third significant change happened during the same period: young people started having sex later. The proportion of young people aged 15-19 who reported not yet starting to have sex rose from 30% to 55% over the 1999-2016 study period.
HIV incidence was steady at 1.17% a year over most of the study period, from 2000 to 2010. But after that it started to fall. By 2012, it was 0.8% a year and by 2016 it was 0.66% a year -- a 42% decline. Incidence fell further in men (by 54%) than in women (by 32%). Grabowski said this might be due to men reaping the benefits both of ART and medical male circumcision.
At the same time, however, prevalence has stayed stuck at a remarkably steady 13% -- exactly what it was in 1994. This is probably due to the fact that ART is prolonging people’s lives, and so the net total of people with HIV in the population is staying the same.
Migrants More at Risk Within Africa
A second study looked at migrants to the Rakai area and compared HIV incidence in them versus permanent residents. Migrants were defined as a person "who moves to a new community with intention to stay." Among the 13,991 people in this study, one-third (4571 people) met this definition.
Annual HIV incidence was 0.88% among permanent residents, 0.97% among long-term settled migrants, and 1.6% among recently arrived migrants.
After statistical adjustment, researchers found that among women, recently arrived migrants were 60% more likely to become infected with HIV than permanent residents, but settled migrants were no more likely. Recently arrived migrant men were 34% more likely to become infected, but this was not statistically significant.
This study confirms that in East Africa, as much as in other parts of the world, being a new arrival within a community is a risk factor for HIV in itself.
MK Grabowski, G Nakigozi, F Nalugoda, et al. Combination HIV prevention and HIV incidence in Rakai, Uganda. Conference on Retroviruses and Opportunistic Infections. Seattle, February 13-16, 2017. Abstract 34LB.
OM Olawore, A Tobian, F Nalugoda, et al. Migration, gender, and HIV incidence in Rakai, Uganda. Conference on Retroviruses and Opportunistic Infections. Seattle, February 13-16, 2017. Abstract 1015.